We just returned from a week-long trip to Paris, France, with our eldest granddaughter. It was Caroline's 16th birthday gift so the trip was more about her enjoying Paris than my taking pictures. Nonetheless, I wanted to be prepared for photo opportunities. I decided not to take my gear in the bag I use at home, the Vanquest VSlinger, which holds a lot of gear for when I'm out and about at home. Instead, I chose a combo of two Lowepro bags I've almost sold off a couple of times: my Fastpack 350 and Passport Sling.
I wanted to carry all of the photo gear I intended to have with me while in Paris in one bag as a carry on yet still have space for other things I wanted to have with me on the flights to and from Europe. These included travel docs, iPad mini, Kindle, real old-fashioned paperback, water bottle, medicine, etc. The Fastpack 350 was a much better alternative for this than the VSlinger. The Fastpack has a rear compartment that will accommodate a 15" laptop, so I was easily able to store my FlashBender reflector and a pouch containing the iPad mini, Kindle, and paperback plus earbuds. 
However, once in the apartment we rented (Perfectly Paris: http://www.perfectlyparis.com - an excellent collection of beautiful apartments with perfect amenities! Check them out!) for the week, I wanted a smaller bag that I could use every day and not break my back. The Passport Sling fills the bill, especially since its inside compartment for one's camera can be removed so the bag itself can be flattened out nicely and packed in checked luggage. I then filled the compartment piece with underwear and socks and packed it in the checked bag as well. Glad I decided on this bag instead of my original choice, the Lowepro Streamline 250 (http://www.infotor.com/blog/rethinking-my-everyday-bag-when-traveling/).
As my everyday bag, the Sling's interior compartment held my E-M1 with 12-40mm mounted on the wide end and my 75-300mm in a Domke Wrap and 25mm + 35-100mm wrapped together (http://www.infotor.com/blog/stacking-lenses-gluing-two-back-caps-to-store-two-lenses/) in another Domke Wrap in the other end of the compartment. This left the swooping front part of the bag available for other things. I stored my Olympus Tough TG-3, a stuffed rain parka (the Patagonia Houdini), a selfie stick, and one of my small Eagle Creek bags containing hearing aid batteries, band-aids, and other like essentials there. Plus, if needed, I could have unzipped and expanded this front area, but I resisted doing this. The Sling also has two small, interior pockets into which I was able to slip my two spare E-M1 batteries and two TG-3 batteries. In the rear-most exterior pocket I stored my water bottle and a dSLR size GorillaPod (which I never used!). Side pockets were perfect for easy access to street map and Metro/Bus map.
Though the Sling worked perfectly, the reality of our daily outings was that I never used any of my other lenses! Now, to be fair, this trip was not about getting great iconic shots or creative shots of of iconic Paris sights. It was about taking pictures of Caroline visiting Paris with a few iconic shots thrown in. Had I been on my own or on a mission to get those other shots and do more street photography experimentation as well as reworks of traditional sightseeing shots, I would probably switched lenses now and then. However, as it turned out, I would have been fine using the smaller Lowepro Streamline 250 as my day bag. Lesson learned for future trips. Another reality was that there were days when I rarely even took my E-M1 out of the bag! At home and having just off-loaded all of my pictures into Lightroom, I see that I almost took an equal number of pictures with each of the cameras I had with me: E-M1, Olympus Tough TG-3, and my iPhone 6 using ProCamera app! About 250 each.
The real lesson, though, of this experience is that when you are ready to sell or give away an old bag...STOP! You never know if it may come in handy down the road.
Please leave me questions or comments on my Facebook page (https://www.facebook.com/billbooz) or on Google+ (http://plus.google.com/+BillBooz). I look forward to interacting with you! Check out my free eBook on Mastering Your Camera's Priority Modes: http://www.infotor.com/ebooks. Download and enjoy! In addition to offering scheduled, hands-on photography classes periodically, I am also available to do one-on-one tutoring or small group lessons designed to meet YOUR needs and what you want to learn in the area of photography, using flashes, or the use of Apple products and software. Give yourself the gift of learning: http://www.infotor.com/photoclasses! And check out my tutoring bundle: http://www.infotor.com/photoclasses/tutoringbundle.php as well. A PDF of my brochure is at http://www.infotor.com/photoclasses/brochures/WHBI-Brochure_2015.pdf.